1. Field of the Invention
The present invention relates to a semiconductor device. In particular, the present invention relates to a switching power supply circuit.
2. Description of the Background Art
In a switching power supply circuit as one of semiconductor devices, an error between a voltage obtained by division of an output voltage by a serial resistive element and a predetermined reference voltage is amplified with an error amplifier. On the basis of the error, On-Duty of a switching element is controlled with a PWM (Pulse Width Modulator) comparator, to keep an output voltage value constant. Thus, it is possible to obtain a desired direct current voltage from an input direct current voltage.
It is to be noted that conventional techniques regarding the switching power supply circuit are disclosed in, for example, Japanese Patent Application Laid-Open Nos. 2001-86740, 2003-52170 and 2004-80985.
As thus described, in the switching power supply circuit, an output voltage is fed back to the error amplifier to control the output voltage. Incidentally, in the switching power supply circuit, a low-pass filter circuit including an inductor and a capacitor is connected between an input terminal and an output terminal. Therefore, according to the configuration where the output voltage is fed back to the error amplifier, the aforementioned inductor and capacitor are included in the feedback loop. For this reason, there is a problem in that a phase of an open loop as a whole of the power supply circuit in a resonance frequency of the inductor and the capacitor changes by about 180°, which causes a phase margin to be lost, leading to oscillation of the circuit.